The principle and method of waterproof and airtightness testing

Introduction to the working principle of new non-destructive gas detection:

The detection system of the airtightness leak detector, as the name suggests, uses the pressure drop method to determine the leakage rate, leakage value, etc. through a series of sampling, calculation, and analysis carried out by the precision testing instrument system through equal intake, stabilization, detection, and then detection of gas pressure and volume changes. Based on these data, a judgment of OK or NG is made. Mainly used for waterproof testing of small household appliances, airtightness testing of medical devices, and leakage testing of stainless steel containers. The principle of this method for leak detection is to introduce a certain volume of gas with a certain pressure into a closed workpiece chamber, let it stand for a period of time to stabilize its pressure, then disconnect the compressed air supply to the component (valve closed), and measure the pressure change after a predetermined measurement time. If there is a leak, the sensing pressure will decrease.

Pressure drop method – differential pressure (positive and negative pressure) direct airtightness leak detection method

Mainly used for sealing testing of valves and fittings, airtightness testing of stainless steel welding products, and sand hole micro leakage testing of aluminum alloy die-casting products. The principle is similar to the pressure drop method, but the method is better. Inject a certain pressure of gas into the enclosed workpiece chamber, and at the same time, introduce the same pressure of gas into a standard tank. After a period of rest, observe the pressure inside the standard tank and the small pressure difference generated on the differential pressure sensor due to leakage of the workpiece. The leak detector quantitatively calculates the leakage amount of the measured object based on the output change of the differential pressure sensor. The existence of benchmarks minimizes the impact of testing on external environment and work itself. Overcoming the shortcomings of the above methods, the efficiency, accuracy, and reliability of airtightness testing have been improved.

Suitable for testing scenarios with low requirements. For example, IP waterproofing testing, such as waterproofing testing for outdoor electrical products, involves compressing one side of the chamber and collecting leaked gas on the other side (chamber) while minimizing the chamber volume to increase the rate of pressure change per unit of leakage.

Indirect detection of differential pressure (positive and negative pressure) using pressure drop method

Mainly used for sealing detection of valves and fittings, leakage detection of stainless steel welding products, and sand hole micro leakage testing of aluminum alloy die-casting products. The principle is similar to the pressure drop method, but the method is better. Inject a certain pressure of gas into the enclosed workpiece chamber, and at the same time, introduce the same pressure of gas into a standard tank. After a period of rest, observe the pressure inside the standard tank and the small pressure difference generated on the differential pressure sensor due to leakage of the workpiece. The airtightness detector quantitatively calculates the leakage amount of the measured object based on the output change of the differential pressure sensor. The existence of benchmarks minimizes the impact of testing on external environment and work itself. Overcoming the shortcomings of the above methods, the efficiency, accuracy, and reliability of detection have been improved.

Suitable for testing scenarios with low requirements. For example, IP waterproof testing, such as outdoor electrical products, involves compressing one side of the chamber and collecting leaked gas on the other side (chamber) while minimizing the chamber volume to increase the rate of pressure change per unit of leakage.

The flow detection method of the airtightness leak detector adopts the method of instantaneous loss of flow to conduct a sealing test on the tested product. The main principle of airtightness testing is that the sensor directly detects the leakage rate of the product and displays it in real time, which can basically save the accumulated time of leakage testing in the original pressure leakage testing method. This product has a fast leakage testing speed and can directly display the leakage unit, making it suitable for products that require testing efficiency. The measurement signal of flow measurement is independent of the test volume, unlike in pressure measurement where the measurement signal decreases with the increase of the test volume. This is an advantage in calibration, as the measurement signal directly corresponds to the gas flow rate passing through the leakage calibrator. During the calibration process, there is no need to know the exact test volume or consider determining the leakage rate. The volumetric flow method is generally not used for leak detection but for flow control. For example, before conducting a pressure drop leak test using the same measuring element (differential pressure sensor), the free channel in the gas system is monitored for flow. In the mass flow detection method, the test signal is not only independent of the test volume and pressure, but also directly corresponds to the standard leakage rate Std cm3/min, which is different from the pressure drop method where the allowable leakage rate needs to be calculated.

The volumetric flow method is generally not used for airtightness testing but for flow control. For example, before conducting a pressure drop leakage test using the same measuring element (differential pressure sensor), the free channel in the gas system is monitored for flow.